Don’t convert to string when we want the raw SVG buffer.

src/format-hooks/svg.js

@@ -4,7 +4,7 @@ module.exports = async function createSvg(sharpInstance) {
   let input = sharpInstance.options.input;
   let svgBuffer = input.buffer;
   if(svgBuffer) { // remote URL already has buffer
-    return svgBuffer.toString("utf-8");
+    return svgBuffer;
   } else { // local file system
     return fsp.readFile(input.file);
   }